Hyponatremia

Background

• Low = <135meq/L
• Symptomatic = <120meq/L (may be higher if occurs abruptly)
  • N/V
  • Anorexia
  • Muscle cramps
  • AMS
  • Sz (esp if Na < 113)
  • Coma
• Rapid correction can cause CHF & CPM (AMS, dysphagia, dysarthria, paresis)

Diagnosis

• Must determine volume status and calculated osm
  • In true hyponatremia the osm is reduced

DDX

1. Hypertonic hyponatremia (osm > 295)
   1. Hyperglycemia
   2. Mannitol excess
2. Isotonic (pseudo) hyponatremia (osm 275-295)
   1. Hyperlipidemia
   2. Hyperproteinemia
3. Hypotonic hyponatremia (osm < 275)
   1. Hypovolemic
      1. Renal
         1. Diuretic use
         2. Na-wasting nephroathy (RTA, CRF)
         3. Osmotic diuresis (glucose, urea)
         4. Aldosterone deficiency
      2. Extra-renal
         1. GI loss
         2. 3rd space loss
            1. Burns
            2. Pancreatitis
            3. Peritonitis
   2. Hypervolemic
      1. Urinary Na > 20
         1. Renal failure
      2. Urinary Na < 20
         1. CHF
         2. Nephrotic syndrome
         3. Cirrhosis
   3. Euvolemic (urine Na usually > 20)
      1. SIADH
         1. Pain, stress, nausea
      2. Hypothyroidism
      3. Drugs
         1. NSAIDs, sulfonylureas
      4. H20 intoxication
      5. Glucocorticoid deficiency

Treatment

1. Correct volume deficit (NS)
2. For severe (<120 with CNS changes):
   1. 3% NS @ 100 cc/hr x 3 hrs (70kg person)
3. For non-70kg person:
   1. (kg X 0.6)/513 = cc/hr 3%
4. For seizure, benzos + bolus 1.5cc/kg of 3% over 10min; repeat Q10min until sz stops (max total = 6cc/kg)

NA DEFICIT

1. Na Deficit (meq) = kg x 0.6 x (140 - Na)
2. Give 1/3 total def rapidly in severe sx
3. OR (Desired Na - Measured Na)(0.6)(wt in kg)= mEq Na administered

• NS = 154 meq/L
• 3% = 513 meq/L

EXAMPLE

desired Na- 120

measure Na- 100

(120-100)(.6)(70kg)=840 meq

^if 513meq in 1L, then 840 meq in 1.6L. Correct over 24hr, so 68cc hypertonic Na/ hr for 24 hrs

Asympt = max inc 0.5meq/L/hr (12meq/L/dy)

Sympt = 1-2 meq/L/hr

^Do not correct to >120 meq/l or >20 meq/l in 24 hr

Disposition

Admit Na < 125

Source

2/4/06 DONALDSON (adapted from Tintinalli, Mistry)